Species richness of annual legumes in relation to grazing in Mediterranean vegetation in northern Israel

Abstract

Species richness of annual legumes in step-point transects was analyzed for 79 pairs of grazed and ungrazed sites of Mediterranean vegetation in northern Israel. Seventy-eight species of annual legumes belonging to 17 genera were sampled. Species richness of all annual legumes of Medicago and Trifolium was significantly greater, by 25-42%, on the grazed compared to the ungrazed site of site-pairs. Legume richness was significantly greater on Cretaceous and Eocene sedimentary rocks compared to younger Neogene and Pleistocene sediments, with intermediate richness on basalt. It was significantly lower in sites with 400-500 mm rainfall compared to 500-900 mm, and in wetland compared to grassland, shrubland, and woodland. Species richness of annual legumes, Medicago and Trifolium, increased significantly from zero or low grazing intensity to high intensity. A consistent, not significant reduction of species richness was observed at extremely high grazing intensity. Many species of small annual legumes increased in cover with grazing intensity. Erect or twining species did not show this response. The tendency of increased richness of annual legumes with grazing was confirmed for subhumid Mediterranean communities, but it may be reversed at extremely high grazing intensities, or in semiarid communities grazed by sheep, and for some legume taxa. Management for in situ conservation of the entire annual legume flora in productive Mediterranean vegetation requires, in different parts of the landscape, continuation of intense grazing and relative protection from grazing.